You may have this creature enter as a copy of any creature on the battlefield, except it enters with X additional +1/+1 counters on it.
Legal in
Pioneer, Modern, Legacy, Vintage, Penny, Commander, Oathbreaker, Brawl, Historic, Timeless
Rulings (9)
You can choose not to copy anything. In that case, Altered Ego enters as a 0/0 creature and is probably put into the graveyard immediately. It won't have +1/+1 counters placed on it by its ability.
2025-01-24
Any "enters" abilities of the copied creature will trigger when Altered Ego enters the battlefield. Any "as [this creature] enters" or "[this creature] enters with" abilities of the chosen creature will also work.
2025-01-24
If Altered Ego somehow enters at the same time as another creature, Altered Ego can't become a copy of that creature. You may choose only a creature that's already on the battlefield.
2025-01-24
If the chosen creature is copying something else (for example, if the chosen creature is another Altered Ego), then your Altered Ego enters as whatever the chosen creature copied.
2025-01-24